The mechanisms by which muscle cells construct thick filaments of precise dimensions from myosin and associated proteins under biological regulation are the central focus of this proposal. The structure and assembly of thick filaments of the nematode, Caenorhabditis elegans are studied because of the continuing usefulness of mutants in uncovering new information and the increasing store of genetic, molecular and cellular information about this organism and its muscles. The first aim is to complete current work on the macromolecular composition of the thick filaments. Resolution of the components of the core structures within the filament backbones is a major goal. The localization of these and other macromolecular components in addition to the established two myosins and paramyosin by the development and use of specific antibodies will complete this aim. The second aim will pursue partial reconstitution of nematode thick filaments from previously dissociated myosin, paramyosin and core structures. The establishment of conditions for depolymerization and repolymerization of isolated core structures will complete this aim. The third aim concerns the newly discovered assemblages of multiple thick filament-related structures that are enriched in specific nematode mutants. Do the distributions of the two myosins and paramyosin change with time? Can isolated assemblages produce thick filaments in vitro? What are the biochemical requirements in terms of specific proteins and cofactors for either dynamical change? The fourth aim is an analysis of additional mutants by the kinetic results of the third aim so as to potentially order genetically specified functions with respect to the sequence of events in thick filament assembly. Further, the effects upon assembly of genetically altering the amounts of specific filament components synthesized will be monitored. The understanding of the mechanisms for assembly of thick filaments in C.elegans is directly relevant to development, physiological and pathological problems in human skeletal muscle and provides useful models for the roles of gene products in the morphogenesis of differentiated tissues that are important in many inherited human diseases.